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| | ==Equine Guttural Pouch== | | ==Equine Guttural Pouch== |
| | [[Image:Equine Guttural Pouch.jpg|thumb|right|150px|Equine Guttural Pouch - Copyright David Bainbridge]] | | [[Image:Equine Guttural Pouch.jpg|thumb|right|150px|Equine Guttural Pouch - Copyright David Bainbridge]] |
| − | *The guttural pouch is an anatomical structure that is only found in the horse (and other perissodactyla). | + | *The [[Guttural Pouches - Anatomy & Physiology|guttural pouch]] is an anatomical structure that is only found in the horse (and other perissodactyla). |
| − | *The guttural pouches are paired ventral diverticulae of the eustachian tubes, formed by escape of mucosal lining of the tube through a relatively long ventral slit in the supporting cartilages.
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| − | *Each pouch attains a capacity of 300-500ml and is air-filled.
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| − | *The stylohyoid bone partially divides each of the guttural pouches into lateral and medial compartments - the medial compartment being approximately double the size of the lateral one and extends further caudally and ventrally.
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| − | ===Surrounding Gross Anatomy===
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| − | - '''Dorsal to Guttural Pouch''': ventral surface of the skull/the wing of atlas.
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| − | - '''Ventral to Guttural Pouch''': pharynx and beginning of oesophagus; medial retropharyngeal lymph node between pharynx and ventral wall of pouches.
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| − | - '''Lateral to Guttural Pouch''': pterygoid muscles, and parotid and mandibular salivary glands.
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| − | - '''Medial to Guttural Pouch''': right and left pouches separated dorsomedially by rectus capitis ventralis and longus capitis muscles; below this by fused walls of the two pouches forming the median septum.
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| − | ===Blood Vessels and Nerves===
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| − | Several cranial nerves and arteries lie directly against the pouch as they pass to and from foramina in the caudal part of the skull (vessels within mucosal folds that indent the pouches):
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| − | *'''Medial Compartment''':
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| − | - Cranial nerves IX, X, XI, XII.
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| − | - Continuation of the sympathetic trunk beyond the cranial cervical ganglion.
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| − | - Internal carotid artery.
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| − | *'''Lateral Compartment''':
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| − | - Cranial nerve VII - limited contact with the dorsal part of the compartment.
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| − | - External carotid artery crosses the lateral wall of the lateral compartment in its approach (as maxillary artery) to the atlas canal. The external maxillary vein is also visible.
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| − | The pouch also directly covers the temporohyoid joint.
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| − | ===Drainage===
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| − | *Natural drainage of the pouch is throught the slit-like (pharyngeal) openings of the eustachian tube in the lateral wall of the nasopharynx.
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| − | *The connection opens when the horse swallows and grazing normally provides drainage. However, most of the pouch is ventral to his slit, and therefore drainage may be rather ineffective. If blocked, secretions accumulate and the pouch distends producing a palpable swelling.
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| − | ===Clinical Conditions===
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| − | 1. '''Guttural Pouch Empyema''':
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| − | - Purulent material in pouch. Respiratory infections can extend into the pouches from the pharynx or from retropharyngeal lymph nodes.
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| − | - Secretion/pus accumulates. The pouch distends forming a palpable, fluctuating visible swelling behind the jaw.
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| − | - Seen as a fluid line in standing lateral radiograph of guttural pouches. Can be surgically drained or with catheter.
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| − | - Material can become chondroid - hard concretions of pus - removed by surgery.
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| − | 2. '''Guttural Pouch Mycosis''':
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| − | - Fungal infections (Aspergillosis).
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| − | - Typically affect caudodorsal medial compartment.
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| − | - Signs: painful swelling in parotid region, abnormal carriage of head and neck, nasal discharge, and the horse may be head shy.
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| − | - Erosion of the roof of the guttural pouch produces a variety of signs by damage to important structures directly related to the pouch:
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| − | a) ''Epistaxis'': nasal bleeding. Erosion of internal carotid artery severe, maybe even cause fatal haemorrhage.
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| − | b) ''Dysphagia'': difficulty in swallowing. Paresis of the pharynx and soft palate is caused by lesions involving the glossopharyngeal and vagus nerves.
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| − | c) ''Laryngeal Hemiplegia'': roaring - following vagus involvement.
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| − | d) ''Horner's Syndrome'': nasal congestion, drooping of upper eyelid, miosis, sweating and hyperaemia on same side of face. From involvement of sympathetic nerve (cranial cervical ganglion).
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| − | e) ''Facial Paresis'': rare.
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| − | f) ''Tongue Paralysis'': rare.
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| − | g) ''Vestibular Signs'' and ''Arthritis'': alanto-occipital joint - very rarely.
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| − | 3. '''Guttural Pouch Tympany''':
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| − | - Foals up to one year of age. The guttural pouch fills with air, but cannot escape through the pharyngotubal opening (acts as a one-way valve allowing air to be drawn into the pouch, but not expelled from it). Usually there is no gross abnormality of the opening.
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| − | - Visible external swelling and large pouch on radiographs.
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| − | - Consequences: collapse of pharyngeal roof, and therefore dysphagia.
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| − | - Unilateral tympany can be treated by forcing an opening in the median septum (fenestration) so that both pouches communicate with the pharynx through a single opening.
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| − | - Bilateral tympany - parts of the flaps guarding the openings may have to be removed.
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| − | ===Inspection/Imaging of the Pouches===
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| − | 1. Visual observation and palpation.
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| − | 2. Radiography.
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| − | 3. Endoscopy - performed by passing an endoscope tube through the ventral nasal meatus and into the pharyngeal opening of the eustachian tube, and thus into the guttural pouches. Draining can be performed by passing a catheter along the same route.
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| − | 4. Ulstrasonography.
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| − | 5. Open surgery - best under general anaesthetic - three routes of access:
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| − | - '''''Viborg's Triangle''''': incision between tendon of the sternocephalicus muscle, linguofacial vein and ramus of mandible. (Distance between triangle and pouch is greatly reduced when pouch is enlarged).
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| − | - '''''Hyovertebrotomy''''': incision ventral to wing of atlas.
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| − | - '''''Modified Whitehouse Approach''''': skin incision ventral to linguofacial vein, then blunt dissection along larynx to guttural pouch.
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| − | ===Function(s)===
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| − | Largely unknown, however hypotheses have been put forward:
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| − | *Influences internal carotid artery blood pressure. Air pressure varies with phase and forcefulness of respiration. Artery in mucosal fold exposed sufficiently to be affected.
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| − | *Cerebral blood cooling mechanism. Operates at times of physical stress, when core body temperature is raised. Vigorous respiration, cool air in guttural pouches, and exposed artery, all leads to cooling of the blood.
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| | ==Histology== | | ==Histology== |